1. Field of the Invention
The present invention relates to a method for color matching using a combination of two or more powder coatings having different colors from each other to give a target color, and a method for producing a coating film.
2. Discussion of the Related Art
A powder coating is prepared by adding several colors of colorants to a resin, a curing agent, an additive, and the like, mixing the components, kneading the resulting mixture in a molten state, and subsequently cooling and pulverizing the mixture, and optionally classifying the particles by size. Generally, when two or more powder coatings having different colors from each other thus prepared are applied in a mixture, the coating film obtained appears macroscopically to be uneven (this appearance is hereinafter referred to as “mottling”). For this reason, a coating need to be supplied for each color needed so that a vast number of kinds of coatings have to be furnished.
In order to solve this problem, for the sake of simplifying the method for color matching using powder coating, there has been desired the development of a method for color matching to a broad range of colors by combining several colored powders.
Japanese Unexamined Patent Publication No. Hei 4-504431 proposes a method capable of applying a powder having a particle size of which color differences are visually indistinguishable, i.e., a maximum particle size of 10 μm or less, comprising granulating the powder so that particles having different colors are not segregated, and applying the granules using an ordinary electrostatic coating machine. However, the production steps are complicated because the powder coating is pulverized to a particle size of 10 μm or less, and granulated.
Japanese Patent Laid-Open No. Hei 11-293160 proposes a method comprising carrying out dry-blend color matching using plural colored translucent powder coatings containing a coloring agent and a clear translucent powder coating not containing a coloring agent. However, these translucent coatings are susceptible to affect the color of the substrate to be coated.
European Patent Publication No. 724611 proposes a method of special coating comprising mixing several colored thermosetting powder coatings containing a “bleeding” dye or pigment. However, since the dye or pigment used is likely to “bleed,” the coating film obtained is likely to be faded by the solvents, and the “two-coat two-bake” treatment is required, thereby making the coating process complicated.
Also, Japanese Patent No. 2899966 proposes a method using a powder coating that does not thermally cure alone at temperatures of 250° C. or less but is thermally cured at temperatures of 250° C. or less when mixed with another kind of powder coating, and applied. Although an effect can be obtained to a certain extent, further improvements have been desired.
An object of the present invention is to provide a method for color matching using a combination of two or more powder coatings having different colors, thereby giving a coating film having homogeneous color with low mottling as a simplified process for color matching using the powder coatings, and a method for producing a coating film.
These and other objects of the present invention will be apparent from the following description.